实验6

#include <stdio.h>
#define N 4

int main() {
	int x[N] = {1, 9, 8, 4};
	int i;
	int *p;
	for (i = 0; i < N; ++i)
		printf("%d", x[i]);
	printf("\n");
	for (p = x; p < x + N; ++p)
		printf("%d", *p);
	printf("\n");
	p = x;
	for (i = 0; i < N; ++i)
		printf("%d", *(p + i));
	printf("\n");
	p = x;
	for (i = 0; i < N; ++i)
		printf("%d", p[i]);
	printf("\n");
	return 0;
}

　　

 

#include <stdio.h>
#define N 4

int main() {
	char x[N] = {'1', '9', '8', '4'};
	int i;
	char *p;
	for (i = 0; i < N; ++i)
		printf("%c", x[i]);
	printf("\n");
	for (p = x; p < x + N; ++p)
		printf("%c", *p);
	printf("\n");
	p = x;
	for (i = 0; i < N; ++i)
		printf("%c", *(p + i));
	printf("\n");
	p = x;
	for (i = 0; i < N; ++i)
		printf("%c", p[i]);
	printf("\n");
	return 0;
}

　　

2001;2001

 

#include <stdio.h>

int main() {
	int x[2][4] = { {1, 9, 8, 4}, {2, 0, 2, 2}} ;
	int i, j;
	int *p;
	int (*q)[4];
	for (i = 0; i < 2; ++i) {
		for (j = 0; j < 4; ++j)
			printf("%d", x[i][j]);
		printf("\n");
	}
	for (p = &x[0][0], i = 0; p < &x[0][0] + 8; ++p, ++i) {
		printf("%d", *p);
		if ( (i + 1) % 4 == 0)
			printf("\n");
	}
	for (q = x; q < x + 2; ++q) {
		for (j = 0; j < 4; ++j)
			printf("%d", *(*q + j));
		printf("\n");
	}
	return 0;
}

　　

 

#include <stdio.h>

int main() {
	char x[2][4] = { {'1', '9', '8', '4'}, {'2', '0', '2', '2'} };
	int i, j;
	char *p;
	char (*q)[4];
	for (i = 0; i < 2; ++i) {
		for (j = 0; j < 4; ++j)
			printf("%c", x[i][j]);
		printf("\n");
	}
	for (p = &x[0][0], i = 0; p < &x[0][0] + 8; ++p, ++i) {
		printf("%c", *p);
		if ( (i + 1) % 4 == 0)
			printf("\n");
	}
	for (q = x; q < x + 2; ++q) {
		for (j = 0; j < 4; ++j)
			printf("%c", *(*q + j));
		printf("\n");
	}
	return 0;
}

　　

2001;2004

 

#include <stdio.h>
#include <string.h>
#define N 80

int main() {
	char s1[] = "C, I love u.";
	char s2[] = "C, I hate u.";
	char tmp[N];
	printf("sizeof(s1) vs. strlen(s1): \n");
	printf("sizeof(s1) = %d\n", sizeof(s1));
	printf("strlen(s1) = %d\n", strlen(s1));
	printf("\nbefore swap: \n");
	printf("s1: %s\n", s1);
	printf("s2: %s\n", s2);
	printf("\nswapping...\n");
	strcpy(tmp, s1);
	strcpy(s1, s2);
	strcpy(s2, tmp);
	printf("\nafter swap: \n");
	printf("s1: %s\n", s1);
	printf("s2: %s\n", s2);
	return 0;
}

　　

strlen(s1)计算字符串中的字符个数，而sizeof(s1)计算的事对象所占的内存空间

13

不可以替换

是

 

#include <stdio.h>
#include <string.h>
#define N 80

int main() {
	char *s1 = "C, I love u.";
	char *s2 = "C, I hate u.";
	char *tmp;
	printf("sizeof(s1) vs. strlen(s1): \n");
	printf("sizeof(s1) = %d\n", sizeof(s1));
	printf("strlen(s1) = %d\n", strlen(s1));
	printf("\nbefore swap: \n");
	printf("s1: %s\n", s1);
	printf("s2: %s\n", s2);
	printf("\nswapping...\n");
	tmp = s1;
	s1 = s2;
	s2 = tmp;
	printf("\nafter swap: \n");
	printf("s1: %s\n", s1);
	printf("s2: %s\n", s2);
	return 0;
}

　　

存放的是"C, I love u."的地址，sizeof计算的是s1所占的内存空间，strlen计算的是字符串的字符个数

可以替换

交换的是地址，没有交换

 

#include <stdio.h>
#include <string.h>
#define N 5
int check_id(char *str);

int main() {
	char *pid[N] = {"31010120000721656X",
	                "330106199609203301",
	                "53010220051126571",
	                "510104199211197977",
	                "53010220051126133Y"
	               };
	int i;
	for (i = 0; i < N; ++i)
		if ( check_id(pid[i]) )
			printf("%s\tTrue\n", pid[i]);
		else
			printf("%s\tFalse\n", pid[i]);
	return 0;
}

int check_id(char *str) {
	int i;
	if (strlen(str) == 18) {
		for (i = 0; i < 18; ++i) {
			if ((str[i] >= '0' && str[i] <= '9') || str[i] == 'X')
				return 1;
		}
	} else
		return 0;
}

　　

 

 

#include <stdio.h>
#include <string.h>
#define N 80
int is_palindrome(char *s);

int main() {
	char str[N];
	int flag;
	printf("Enter a string:\n");
	gets(str);
	flag = is_palindrome(str);
	if (flag)
		printf("YES\n");
	else
		printf("NO\n");
	return 0;
}

int is_palindrome(char *s) {
	int i, n;
	n = strlen(s);
	for (i = 0; i <= (n / 2); ++i) {
		if (s[i] == s[n - i - 1]) {
			return 1;
		}
		if (s[i] != s[n - 1 - i])
			return 0;
	}
}

　　

 

 

#include <stdio.h>
#define N 80
void encoder(char *s);
void decoder(char *s);

int main() {
	char words[N];
	printf("输入英文文本: ");
	gets(words);
	printf("编码后的英文文本: ");
	encoder(words);
	printf("%s\n", words);
	printf("对编码后的英文文本解码: ");
	decoder(words);
	printf("%s\n", words);
	return 0;
}

void encoder(char *s) {
	int i;
	for (i = 0; i < N; ++i) {
		if (s[i] != 'z' && s[i] != 'Z' && s[i] <= 'z' && s[i] >= 'A') {
			s[i] = s[i] + 1;
		} else if (s[i] == 'z')
			s[i] = 'a';
		else if (s[i] == 'Z')
			s[i] = 'A';
	}
}

void decoder(char *s) {
	int i;
	for (i = 0; i < N; ++i) {
		if (s[i] != 'a' && s[i] != 'A' && s[i] <= 'z' && s[i] >= 'A') {
			s[i] = s[i] - 1;
		} else if (s[i] == 'a')
			s[i] = 'z';
		else if (s[i] == 'A')
			s[i] = 'Z';
	}
}